Construction Of A Genetic Linkage Map And Mapping QTL Of Important Agronomic Traits Using DH Population In Non-heading Chinese Cabbage (Brassica Campestris Ssp.chinensis)

Non-heading Chinese cabbage {Brassica campestris ssp. chinensis) is originated from China, which is one of the important vegetables in eastern Asia and play an important role in daily menu. Construction of genetic map and QTL mapping will provide an available reference to genetic breeding and molecular marker assisted selection in non-heading Chinese cabbage. The results are shown as follows:Several key factors affecting isolated microspore culture in non-heading Chinese cabbage were studied by mono-factor and multi-factor experimental designs. The results of mono-factor experiments were shown as follows: there were significant differences in the frequency of microspore-induced embryos among 54 genotypes, whose genotypes were classified into four levels; for the low temperature treatment, no significant differences had been found; there were no significant differences under high temperature when the incubation time was within 12～60 h; the addition of NAA and the 6-BA in NLN medium had no significant influence on the frequency of microspore-induced embryos, and if the concentration was excessive, the frequency would decrease; the presence and concentration of activated charcoal had a great influence on the frequency of microspore-induced embryos. Moreover, as indicated by analysis results of genotypes, NAA, 6-BA and activated charcoal concentrations, there were significant differences among different genotypes and activated charcoal concentrations respectively as well as interaction of these two factors, while other interactions remained non-significant.A genetic linkage map of non-heading Chinese cabbage was constructed, which was based on a DH (doubled haploid) population with 112 individuals derived from a F₁ hybrid variety 'Shulv'. Four kinds of markers of SRAP, SSR, RAPD and ISSR were adopted and 186 polymorphic markers including 114 SRAP, 33 SSR, 24 RAPD and 15 ISSR markers were integrated into the resulted map using Mapmaker 3.0 version. This map consisted of 14 linkage groups, covering 1 116.9 cM with a mean marker interval of 6.0 cM. Various linkage groups were featured by 4-27 maker numbers, 30.3-165.8 cM length and 3.4-11.1 cM mean marker interval.By using composite interval mapping (CIM) method, a molecular genetic map with 186 markers was adopted to map and analyze QTL for the quality-related traits including vitamin C, soluble sugar, soluble protein, coarse fibrin, dry weight in leaves and weight ratio between the leaf and the leafstalk in non-heading Chinese cabbage. Two QTL were detected for soluble protein, three QTL for dry weight and four QTL for weight ratio between the leaf and the leafstalk, while no QTL were detected for controlling vitamin C, soluble sugar and coarse fibrin.Based on composite interval mapping (CIM) method., a genetic linkage map with 186 molecular markers was employed in mapping QTL for two cold-tolerant traits in non-heading Chinese cabbage Four QTL controlling electric conductance were detected in LG1, while seven QTL of cold damage index were detected in three LGs. The results of QTL mapping of relative electric conductance and cold damage index were compared and analyzed, as well as the explained variance and the additive effect of these QTL were estimated.A genetic linkage map with 186 molecular markers was adopted in dynamic mapping QTL for morphological traits including the plant height, plant width and the leaf index at eight different growth stages in non-heading Chinese cabbage. A total of eight unconditional QTL for the plant height were mapped in four linkage groups at eight growth stages. As revealed by results, only one unconditional QTL for plant height was detected at all eight stages, others were detected at one or several stages respectively. The explained variance of each unconditional QTL was more than 10%. Twelve conditional QTL for the plant height were detected in six linkage groups at six stages except the first stage. These conditional QTL did not emerge in detecting the unconditional QTL. The explained variance of eight in twelve conditional QTL was more than 10%. For plant diameter, a total of seventeen unconditional QTL were detected in eight linkage groups at eight growth stages. Among these unconditional QTL, none was detected at all growth stages, just at one or several stages respectively. The explained variance of single QTL was more than 10% except two of them. Ten conditional QTL for plant diameter were detected in five linkage groups at four stages except the first stage. The explained variance of six in ten conditional QTL was more than 10%. For the leaf index, a total of twenty-one unconditional QTL was detected in seven linkage groups at eight growth stages. Just one of them was detected at all eight stages, others were detected at one or several stages respectively. The explained variance of fourteen in twenty-one unconditional QTL was more than 10%. Five new conditional QTL for the leaf index were detected in five linkage groups at four stages expect the first stage. The explained variance of four in five conditional QTL was more than 10%.